A Comparison of Two Models for the Separation of Direct and Diffuse Irradiance in Plane of Array

For advanced automated operational monitoring of Photovoltaic (PV) systems, e.g. in order to distinguish losses due to self-shading from malfunctions, direct and diffuse irradiance at the module plane (plane of array, POA) are required separately. However, in practice, usually only measured values of global POA irradiance (GPOA) are recorded on site. There is thus a need for a model to divide GPOA into its direct (IPOA) and diffuse components (DPOA). This paper compares and evaluates two models recently developed that perform such separation. The aim of this work is to show the advantages and disadvantages that these two models offer and how they differ from each other. In order to compare and evaluate them, two different POA data sets were used. The first data set is generated using SolarGIS satellite-based data for 16 different locations across Germany. The second data set contains on-site measured DPOA and GPOA data from a PV power plant located in south-west Germany. Results from both models show good matching with satellite-based data from the 16 different locations.